Mobile internet protocol system and registration method on a hand-off event in the same

PURPOSE: A mobile IP(Internet Protocol) system and a registration method when performing a hand-off in the same are provided to prevent the loss of a datagram according to the hand-off by performing the registration of an HA(Home Agent) through a PFA(Previous Foreign Agent) in case that a mobile node is moved from the PFA to an NFA(New FA) and the hand-off is generated. CONSTITUTION: An HA(100) maintains location information of a mobile node(400). A PFA(200) cooperates with the HA(100), transmits data to the mobile node(400), and previously registers the mobile node(400). An NFA(300) cooperates with the HA(100), transmits data to the mobile node(400), and receives the request of a new registration according to the generation of a hand-off by the movement of the mobile node(400). The PFA(200) re-tunnels a tunneled datagram from the HA(100) to the NFA(300). When the mobile node(400) is registered in the HA(100) through the NFA(300), the mobile node(400) is registered through the PFA(200).